Capacitive coupled connectors for gaseous discharge display panels

ABSTRACT

A method and means for connecting the electrodes of a gaseousdischarge display panel to the drive circuits which control the potential across the electrodes and thus the production of the gaseous discharge. It is demonstrated that a capacitive coupling, rather than an ohmic coupling, is practical and beneficial from a maintenance standpoint, since the gas display panel may be more easily replaced.

United States Patent 1 Krembs June 26, 1973 221 Filed:

[ CAPAClTIVE-COUPLED CONNECTORS FOR GASEOUS DISCHARGE DISPLAY PANELS [75] inventor: George M. Krembs, Hyde Park,

[73] Assignee: International Business Machines Corporation, Armonk, N.Y

June 10, 1970 [21] Appl. No.: 44,959

[56] References Cited UNITED STATES PATENTS 3,626,241 l2/l971 Ngo ..3l5/l69X 3,573,542 4/1971 Mayer et a1 315/169 R Primary Examiner-Alfred L. Brody Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak 7] ABSTRACT A methodand means for connecting the electrodes of a gaseous-discharge display panel to the drive circuits which control the potential across the electrodes and thus the production of the gaseous discharge. It is demonstrated that a capacitive coupling, rather than an ohmic coupling, is practical and beneficial from a maintenance standpoint, since the gas display panel may be more easily replaced.

4 Claims, 4 Drawing Figures 34 42 3 8 38 38 38 r 32 38 4 2 54 a r 4. i i f k 44 30 44 40 R36 CAPACITIVE-COUPLEI) CONNECTORS FOR GASEOUS DISCHARGE DISPLAY PANELS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to electrical connectors and more particularly to capacitive-coupled connectors for use with gaseous-discharge display devices.

2. Description of the Prior Art Gaseous-discharge display panels are well known in the prior art. Such devices generally comprise a gas filled envelope which contains a plurality of electrodes arranged in columns and rows thereby producing a matrix. The electrodes are interconnected to associated drive circuits which are used to generate a potential of a magnitude sufficient to cause a discharge in the gaseous space at the. intersection of two such electrodes. This discharge is visible, and thus the panel may be used as a display panel. By appropriately selecting which electrodes are connected to the drive circuits, the location of the discharge may be controlled, and a desired pattern may be displayed.

In the prior art, however, the electrical connection between the electrodes forming the matrix and the driver circuits have been made by ohmic contact, for example, by soldering wires or by the use of connectorblock terminals. Thus, the gas display panel has been physically integrated with the driver circuits. This integration has been disadvantageous from the viewpoint of reliable maintenance since, when the gas panel must be replaced, the ohmic connection must be destroyed and a new one fabricated. This invention offers the desirable attribute of rapid replacement of a gas panel.

Whenever an isolating capacitance is electrically required or desirable, it is also known in the prior art to fabricate couplers with inherent capacitances, whereby the need for an isolating capacitor as an independent circuit element is obviated. Such a fabrication, for example, is disclosed in U.S. Pat. No. 3,223,884, issued Dec. 14, 1965, an entitled Gaseous Discharge Device. Such capacitive couplings, with their concomitant ease of mechanical assembly, have not, however, been employed in those coupling situations where an ohmic connection has been thought to be required, for example, in a gaseous-discharge panel. Such ohmic connections are, in turn, subject to the disadvantages mentioned above.

SUMMARY OF THE INVENTION the back side of the panel. The drive circuits are fabricated on a conventional circuit board having its electrical connections made to land terminals on the back side of the circuit board. The land terminals of both the gas display panel and the circuit board are placed in identical positions so that they align with each other when the gas panel is placed adjacent the circuit board. Moreover, the lands are coated with an insulating layer so that, in effect, a capacitor is formed by the insulating layer between the aligned land terminals.

A capacitive coupling is thus fabricated between the electrodes comprising the gaseous display panel and their associated drive circuits. This capacitive coupling replaces the ohmic connector of the prior art. It offers advantages from a maintenance viewpoint since a gas panel may be rapidly disconnected from its associated drive circuits and, if necessary, a new one connected thereto.

Accordingly, it is an object of this invention to provide between a gaseous discharge display device and its associated drive circuits a coupling which permits rapid replacement of the display panel.

Another object of this invention is to provide between a gaseous discharge display device and its associated drive circuit a coupling which facilitates their electrical interconnection.

A further object of this invention is to provide a capacitive coupling between a gaseous discharge display panel and its associated drive circuits.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram of a matrix employed in a gas panel used in the invention;

FIG. 2 is a cross-sectionalview'illustrating the mechanical connection and capacitive coupling between a gas panel and circuit board containing driver circuits for the panel;

FIG. 3 is a schematic diagram of an equivalent circuit of an individual gas cell; and

FIG. 4 illustrates a transmission line model of one complete colum of gas cells.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a typical matrix of electrodes fora gaseous-discharge display panel of the type which may be employed in the subject invention. A series of first electrodes 10-16 are arranged in columns, and a series of second electrodes 18-24 are arranged in rows. The electrodes are spaced at their intersections. To form a gas panel, the matrix is placed within a gas-filled envelope 25. In operation, a column and a row electrode simultaneously are energized to produce at their intersection a potential of such a magnitude that a discharge occurs through the gas in the space between the electrodes, thereby producing a visible spot of light. If the electrodes are selectively energized, a desired pattern may be generated by the resulting gaseous discharges. A gas panel which may be employed with this invention is more fully described in an article by D.M. Arora et al., entitled Plasma Display Panel A New Device for Information Displays and Storage in the Eighth National Sympoisum, Society for Information Display, published in May, 1967. I

Each electrode of the matrix is connected to a land terminal 26 which is outside the air-tight, gas-filled envelope 25. These land terminalspermit the electrodes to be electrically connected to voltage control means, such as associated drive circuits which control the potential between the electrodes and thus the gaseous discharges. In the prior art, as described above, these elec trical connections have been made by ohmic connectors. It is a function of this invention to provide a capacitive coupling between each electrode and its associated driver circuit.

According to this invention, the driver circuits are fabricated on a circuit board having its electrical connections made to land terminals which may be aligned with the land terminals of the matrix. The lands are then coated with an insulating layer. Thus, when the gas panel and the circuit board supporting the driver circuits are placed adjacent to each other, a capacitive coupling is achieved by each pair of lands and the intermediate insulating layer. If the gas panel and the circuit board are then mechanically coupled together, there is formed an assembly which provides capacitive coupling and rapid disassembly.

A cross-section of such an assembly is illustrated in FIG. 2. A gas panel 30 has been mechanically coupled to a circuit board 32. The mechanical coupling may be achieved, for example, by a plurality of nuts 34 and bolts 36 which clamp together the panel and board. The circuit board supports the driver circuits 38 which provide the potential to the electrodes within the gas panel assembly 30. Electrical connection between each driver circuit 38 and its associated electrode is achieved by the capacitive coupling formed by lands 40 and 42 and the insulating layer 44. The lands 40 are electrically connected to corresponding electrodes of the gas display panel and correspond to the land terminals 26 in FIG. 1. The lands 42 are attached to the circuit board 32 and are electrically connected to the driver circuits 38.

In operation, the capacitive connector couples the RF energy produced by the drive circuits and also passes the write, read, and the erase pulses which are superimposed upon the RF oscillations generated by the drive circuits. The operation of the capacitive connector and the calculation of the desired magnitude of capacitance will now be discussed.

FIG. 3 represents the equivalent circuit of an individual gas cell, i.e., that area between the electrodes at their intersection. C represents the capacitance of the thin insulator separating the electrode from the gas discharge region; C represents the capacitance on the inner wall of the thin insulator due to the space charge accumulated from the discharging gas plasma; R, represents the variable resistance of the gas column; and V represents the variable voltage across capacitance C due to the residual charges. For typical geometrics, C is approximately equal to 3 X picofarads and C, is approximately equal to 80 X 10" picofarads. Therefore, the capacitance C,,, of an unfired cell is determined by the following equations:

Since the capacitance across the cell, i.e., C,,,, is very small for a fired cell, the capacitance of a fired cell C,

is determined by the following equations:

l/c,=1/c.+1/

c,= c./2 z 40 x 10- pf.

FIG. 4 illustrates a transmission line model of one complete column of a matrix ofa gas panel. The capacitor C represents the coupling capacitor associated with that column electrode and is the value which we are trying to estimate. The capacitor C, is the capacitance of the first cell in that column and the capacitor C, is the coupling capacitor associated with the first row. Similarly, C C and C, are the capacitances associated with further cells in the column. The capacitors C, C,. and C, are the coupling capacitors associated with the other rows in the matrix. The equivalent capacitance of one leg in the above tansmission line model is determined by the following equation:

l lea H -1 lea 1 1)/ 1 l) Therefore, the capacitance of the total legs in the transmission line model is determined as follows:

Substituting the values determined above in equations (2) and (4) for the tired and unfired cells for C yields the following results:

To operate the matrix properly with capacitive con nectors, the drive circuitry must not dissipate any significant power or experience a high voltage drop across the connection capacitance, that is, the connection capacitance must be much greater than the capacitance of the driven load. Therefore, to determine the size of the coupling capacitance C let us assume a ten percent voltage drop across the coupling capacitance. Hence, C must be approximately ten times the total capacitance of the driven load. Therefore, for a column in which all cells are unfired, the following equations determine the value of the coupling capacitance:

and similarly, the following equations determine the value for a column in which all cells are fired:

or 500 fired cells. These numbers of cells are typical of gas display devices and a capacitor of 2.8 picofarads can be practically constructed from land terminals whose dimensions are 0.020 inch times 1 inch. Therefore, such a capactivie connector is feasible under present technology.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a gaseous-discharge display device having a gasfilled envelope, a series of first electrodes arranged in columns within said envelope, a series of second electrodes arranged in rows within said envelope and spaced from said first electrodes, and voltage control means coupled to said first and second electrodes for varying the potential between said first and second electrodes, thereby causing a gaseous discharge between said first and second electrodes whereby the gaseous discharge may be produced at selected intersections of said first and second electrodes, the improvement comprising:

a capacitive coupling between said first electrodes and said voltage control means and said second electrodes and said voltage control means for facilitating the connection of said firstand second electrodes to said voltage control means and wherein the physical characteristics of the capacitive coupling are such that the capacitance of said capacitive coupling to a first electrode is substantially greater than the input capacitance of said first electrode.

2. The improvement of claim 1 wherein the physical electrodes and arranged around the periphery of said envelope;

a flat, rigid support member;

voltage control means for varying the potential between said electrodes and affixed to said support member;

a series of-flat terminals electrically coupled to said voltage control means and arranged around the periphery of said support member; and

means for clamping said support member to said envelope for aligning said terminals on said support member with corresponding terminals on said envelope, whereby said aligned terminals form a capactive coupling between said electrodes and said voltage control means.

4. The assembly of claim 3 further comprising an insulating layer between the aligned terminals for increasing the capacitance of said capacitive coupling to such an extent that the potential drop across said coupling is a small percentage of the potential drop across said electrodes. 

1. In a gaseous-discharge display device having a gas-filled envelope, a series of first electrodes arranged in columns within said envelope, a series of second electrodes arranged in rows within said envelope and spaced from said first electrodes, and voltage control means coupled to said first and second electrodes for varying the potential between said first and second electrodes, thereby causing a gaseous discharge between said first and second electrodes whereby the gaseous discharge may be produced at selected intersections of said first and second electrodes, the improvement comprising: a capacitive coupling between said first electrodes and said voltage control means and said second electrodes and said voltage control means for facilitating the connection of said first and second electrodes to said voltage control means and wherein the physical characteristics of the capacitive coupling are such that the capacitance of said capacitive coupling to a first electrode is substantially greater than the input capacitance of said first electrode.
 2. The improvement of claim 1 wherein the physical characteristics of the capacitive coupling are such that the capacitance of said capacitive coupling to a second electrodE is substantially greater than the input capacitance of said second electrode.
 3. A gas panel assembly comprising: a flat, gas-filled envelope; a series of first electrodes arranged in columns within said envelope; a series of second electrodes arranged in rows within said envelope and spaced from said first electrodes; a series of flat terminals electrically coupled to said electrodes and arranged around the periphery of said envelope; a flat, rigid support member; voltage control means for varying the potential between said electrodes and affixed to said support member; a series of flat terminals electrically coupled to said voltage control means and arranged around the periphery of said support member; and means for clamping said support member to said envelope for aligning said terminals on said support member with corresponding terminals on said envelope, whereby said aligned terminals form a capactive coupling between said electrodes and said voltage control means.
 4. The assembly of claim 3 further comprising an insulating layer between the aligned terminals for increasing the capacitance of said capacitive coupling to such an extent that the potential drop across said coupling is a small percentage of the potential drop across said electrodes. 